Axial flow fan



Sept. 2o, 1949.

l. s. RITTER 2,432,597

AXIAL FLOW FAN Filed NOV. 26, 1946 @r 5 i i e PRE SSI/2E VUL UME INVENTOR.

.[P w/v 5. /Q/r TEE Patented Sept. 20, 1949 Irving S. Ritter, Sharon.Mass.. assignor, by

f mesne assignments, to Westinghouse Electric Corporation, a corporationof Pennsylvania Application November 26, 1946, Serial No.l 712,271-

1 This invention relates tolfan systems and relates more particularly tosystems yusing axial iiow fans for pressure ventilation.

By forcing large volumes of outdoor air through the passenger space oftrolley cars, subway cars and other passenger vehicles, it has beenfound feasible to cool such vehicles during hot weather without the useof refrigeration.

Several, spaced, axial flow fans mounted in the ceilings of the vehiclesalong their longitudinal center lines, and arranged to blow the airdownwardly into the vehicles, are generally used for such pressureventilation.

Axial flow fans have pressure-volume characteristics such that there aredips in the characteristic curves in which the 'fans are unstable and inwhich the direction of air moved by them l may be reversed by a changein fan load.

Due to changes in the number of passengers in a vehicle, the opening ofdoors, etc., the load on one of the fans may be such that it may becomeunstable and act to move air in the reverse direction to that desired.This invention provides a control which, when a fan becomes unstable,causes it to speed up so as to operate at a stable 1 Claim. (ci.230-115) 2 a dip l in the curve. the center of which is variously termedthe burble point, the "stalling point or the "pulsatlon point" of thefan. When the volume handled by the fan is shifted for any reason backinto the center of the dip, it becomes unstable and tends to operate oneither side of the\center of the dip thus drawing or blowing airdepending upon which side of the center of the dip it operates.

In passenger cars having fan systems such as illustrated by Fig. 1, thefans act to build up static pressures in the passenger spaces. Due tochanges in the number of passengers in the cars, the assembly of a largenumber of passengers under one fan, or the opening of one or more of thedoors of a car, it has been found that a fan which has been operatingsatisfactorily to blow air into the pointand to deliver the air ithandles, in the right direction.

An object of the invention is to reverse the direction of fluid moved bya fan when due to the fan becoming unstable, it moves the fluid in thewrong direction.

A more definite object of the invention is to speed up a fan forshifting its operating point on its pressure-volume characteristic curvewhen due to a change in loperating condition, it moves the nuid handledby it in the wrong direction.

The invention will now be described with reference to the drawing, ofwhich: c

Fig. 1 is a diagrammatic view illustrating a fan system to which thisinvention applies;

Fig. 2 is a pressure-volume characteristic curve of an axial flow fanused in the system of F18. 1, and

Fig. 3 is a diagrammatic view illustrating a pressure responsive controlfor speeding up'one of the fans of the system for causing it to shiftfrom an unstable operating point to a stable one.v

' Fig. 1 illustrates a trolley car having the three axial iiow fans 5spaced along the longitudinal center of the car and arranged to drawoutdoor air into the space above the ceiling 6 of the car, and to blowthe air downwardly through apertures in the ceiling, into the car.

Fig. 2 illustrates a pressure-volume charac passenger space, suddenlyreverses its direction oi' flow and takes air from the other fans andpasses the ail upwardly instead'of downwardly.

Accordingto this invention, one or more of the fans of the systems.would be equipped with the control of Fig. 3 which includes the pivotedvane 8 in the airstream at the normal suction side of the fan, and whichoperates when the fan blows air backwardly, to move against the contacti to close the electric energizing circuit of the relay l0, causing therelay to pull in its armature Il. The armature Il and the contact I2 arenormally in contact, forming a short circuit across the resistor I3which is in series with the field winding I4 of the fan motor II. Whenthe armature l I is pulled in by the relay I0 as described, the armatureIl moves away from the contact l2, thus opening the short circuit acrossthe resistor I3 and placing same in series with .the field winding Il.This causes the speed of the motor I5 to be increased, and causes thefan to shift its operating point to the right, facing Fig. 2 of thedrawing, of the dip 'l in the characteristic curve.

The relay l0 would be of the time delay type such as a relay having ayilux decayI solenoid,

' which would keep its armature pulled in for some time after thevane 8has moved away from the contact 9 as a result of the fan again movingair l istic curve typical o! the fans of Fig. 1. Thereis so While oneembodiment of the invention has 4 been described for the purpose ofillustration. it increasing its speed when the air ow through it shouldbe understood that the invention is not is rearward, and timing meansfor causing said limited to the exact apparatus and system illus-L.4nrst mentioned means to maintain the increased trated, as modicationsthereof may be suggested speed for a. predetermined time after the airow by those skilled in the art, without departure from 5 is againforward.

the essence of the invention. IRV'ING S. RITTER.

What is claimed is: l A pressure ventilation system having a pluralityREFERENCES CITED of fans for directing air forwardly in Parallel Thefollowing references are of record in the streams and building up an airpressure in the 10 me of this patent; space supplied with air, in whichdue to a change in load on one of the fans, it may become unstableUNITED STATES PATENTS land move air rearwardly, means responsive toNumber Name Date the direction of air flow through said one of said1,085,286 Moss Jan. 27, 1914 fansl for maintaining same at its normalspeed 15 1,210,030 Baumann Dec. 26, 1916 when the air ow through it isforward, and 4for 2,395,657 Dinsmore et al. Feb. 26, 1946

